Starch, the principal reserve polysaccharide in plants, constitutes a substantial portion of the human diet. It is the principal component of most seeds, tubers, and roots and is produced commercially from corn, wheat, rice, tapioca, potato, and other sources. Most commercial starch is produced from corn which is comparatively inexpensive and abundant throughout the world. Wheat, tapioca, and potato starch are produced on a smaller scale and at higher prices.
Starch is a mixture of linear (amylose) and branched (amylopectin). polymers of .alpha.-D-glucopyranosyl units. Natural starch occurs usually as granules composed of both linear and branched starch molecules. However, some starches are composed only of branched molecules, and these are termed waxy starches because of the vitreous sheen of a cut seed surface. Some mutant seed varieties have been produced with starches having up to 85% linear molecules, although most starches have approximately 25% linear and 75% branched molecules.
The milling of corn provides corn starch, which is extensively used in food and non-food applications. Corn may be dry-milled using screening and air classification of particle size, but this process does not completely separate oil, protein, starch, and hull. Better separation is obtained by wet-milling. (A complete description of the milling process may be found in the Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Edition, Volume 21, pages 492-507, 1983.) In the corn-milling operation, the corn is first cleaned by screening to remove cob, sand, and other foreign material, and then by aspiration to remove the lighter dust and chaff. It is then placed in large vats, called steeps, for the steeping process of softening the kernels for milling. Steeping requires a careful control of water flow, temperature (48.degree.-52.degree. C.), sulfur dioxide concentration (about 0.1%), and a pH at 3-4.
In the wet-milling process, the starch suspension may be processed dry and marketed as unmodified corn starch, modified by chemical or physical means, gelatinized and dried, or hydrolyzed to corn syrup. The wet-milling process requires about 20 gallons of water per 100 pounds of corn; this water must be removed before marketing: It is a goal of the present invention to improve the performance of the means employed in the dewatering process to dewater a starch slurry. In other words, by decreasing the moisture content of starch, the effectiveness of the drying process (the final step in starch manufacture) is improved. The final product may then be employed in various industrial uses.
The effective dewatering of starch is desirable in that a starch with a certain dryness, viscosity, etc. is needed for various industrial uses; by reducing the moisture level in the starch, the amount of potential microbiological growth is reduced. The dewatering is carried out by such means as vacuum filter, plate and frame filter, or by centrifugation.